To grapple with these challenges, organizations have adopted a wide variety of approaches that, to varying degrees, address the five general stages of adaptation listed above. Iterative risk management provides a comprehensive framework and set of processes appropriate for addressing adaptation challenges.32,33,34,35,36 The framework includes steps for anticipating, identifying, evaluating, and prioritizing current and future climate risks and vulnerabilities; for choosing an appropriate allocation of effort and resources toward reducing these risks; and for monitoring and adjusting actions over time while continuing to assess evolving risks and vulnerabilities. Risk communication accompanies each of these steps.33,37,38,39 Iterative risk management helps address equity, economics, and other measures of social well-being and supports participatory stakeholder processes, which can enhance transparency and foster defensible decision-making, an important component of successful adaptation efforts.40
Iterative risk management emphasizes that the process of anticipating and responding to climate change does not constitute a single set of judgments at any point in time; rather, it is an ongoing cycle of assessment, action, reassessment, learning, and response.41 The process helps manage risks that are well known, as well as those that are deeply uncertain due to data limitations or the irreducible unpredictability of some aspects of current and future climate.33,42
Iterative risk management is consistent with most of the elements in the many climate adaptation efforts and approaches currently in use,42,43 including climate vulnerability assessment, iterative risk assessment, and adaptive management as often practiced by federal and other land and resource management agencies,44 as well as disaster risk management.45 Using a comprehensive framework helps highlight commonalities and differences across the approaches used by different jurisdictions and sectors, facilitating comparison and learning among their users. It also situates climate adaptation squarely within the broad range of other risk management activities, such as in the financial, engineering, environmental, health, and national security sectors.2
Adaptation Actions to Reduce Risk
Steps to implementing iterative risk management help decision-makers compare and allocate investments and identify incentives for managing and reducing risk. The planning and implementation steps of the generalized adaptation framework combine several types of actions46,47,48,49 that
reduce exposure (for example, reduce the presence of people or assets in locations that could be adversely affected by climate impacts);
reduce sensitivity (that is, lower the degree to which a system is adversely affected by exposure to climate impacts); and
increase adaptive capacity (that is, raise the ability of human and natural systems to prepare for, adjust to, respond to, and recover from experienced or anticipated climate impacts).
For instance, in the time since Superstorm Sandy, New York City has reduced its potential future flood impacts by relocating a limited number of households out of the most flood-prone areas (reduced exposure), raising the height of some structures above the ground so they suffer less damage from any flooding (reduced sensitivity), and training the officials responsible for revising building codes and land-use policies to use the most up-to-date estimates of flood risk (increased adaptive capacity). Enhancing social cohesion—the degree to which those in a community identify with the community and with each other—is also known to increase adaptive capacity, such as the ability to rebound quickly from disasters.50 More broadly, while adaptive capacity often refers only to the targets of adaptation action (such as communities, ecosystems, and infrastructure), “the ability of institutions themselves to adjust and evolve will be key to their ability to manage for change.”51
Different populations also have different exposure, sensitivity, and adaptive capacity based on their access to resources and information, their culture, and the quality of governance. Such consideration can usefully inform decisions about the equitable and just allocation of resources in reducing climate risk.52
Adapting to Current Variability and Preparing for Future Change
Adaptation addresses two timescales: 1) adapting to current variability, which in any particular location may now be different than suggested by the historical record of climate observations, and 2) preparing for future change. This distinction is useful because some decision-makers may not appreciate the extent to which climate has already changed and because these timescales often call for different types of adaptation actions.
Miami Beach is currently raising the level of its roads and building seawalls to reduce current flooding due to higher sea levels, but it is also choosing the height of these new structures, anticipating that sea levels will be even higher in the future.53 New York City and the Federal Emergency Management Agency (FEMA) agreed to develop two sets of flood maps, one showing current risk for the purpose of setting insurance rates and the other for the longer-term purposes of setting building codes and land-use planning.54 The National Park Service, working with the U.S. Army Corps of Engineers, constructed a revetment, or retaining wall, and living shoreline in 2013 to protect the Cockspur Island Lighthouse in Georgia’s Fort Pulaski National Monument against erosion and accelerated sea level rise. The new revetment incorporated a wider base than is currently required, enabling the addition of rock to extend its height as sea levels rise in the future.55 The State of Louisiana’s Coastal Protection and Restoration Authority’s 2017 Coastal Master Plan has more than 100 structural and coastal restoration projects designed to provide benefits over the next decade and up to 50 years into the future.56
These timescale differences relate to the ubiquitous term resilience57 that is frequently employed in adaptation planning under a spectrum of meanings.58,59 These range from the ability to withstand and recover from current shocks and stressors while retaining basic functions under conditions of existing and near-term variability to the ability to transform in desirable ways over time as the magnitude of change increases.60,61,62,63,64,65 Recognizing these timescales in planning, and communicating expectations for change along those timelines, can also help communities maximize benefits in the near term and identify the most important opportunities for longer-term well-being and resilience.
Organizations are increasingly exploring alternative approaches for replacing the assumption of an unchanging (or stationary) climate in their risk management activities. Vulnerability assessments, a common practice among managers of public lands and natural areas, often evaluate exposure, sensitivity, and adaptive capacity, and provide rankings of the seriousness of various climate risks. Multi-objective approaches, such as structured decision-making,66 explicitly include multiple measures of well-being in risk assessment and management, often in difficult areas such as protecting cultural resources.40 Scenarios are used to 1) assess risks over a range of plausible futures that include both changes in socioeconomic trends as well as climate and 2) choose adaptation actions robust over this wide range of futures.18 California’s 2018 Sea-Level Rise Guidance includes probabilistic sea level rise projections and a worst-case scenario, then integrates both with an adaptive pathways approach67 that encourages robust and flexible plans that can adjust over time if seas rise faster than expected.
Climate risk management requires addressing socioeconomic (for example, future economic, technology, and regulatory conditions) as well as climate uncertainties. Risk management can address such uncertainties, even when they are difficult to characterize with confidence (Ch. 17: Complex Systems, KM 3).42,68,69,70,71 The water sector is pioneering approaches for incorporating such information in water utility adaptation, including scenarios and other robust decision methods aimed at making successful decisions insensitive to a wide range of uncertainty.72 Some agencies are beginning to combine both multi-objective and multi-scenario approaches in quantitative tools that identify vulnerabilities and evaluate tradeoffs among adaptive pathways, seeking risk management strategies that perform well across multiple scenarios and measures of well-being.73,74,75,76 Implementing such methods can require a more complete set of system models than some agencies commonly use in their planning routines, though such tools are becoming increasingly available.77
Benefits of Adaptation Can Exceed the Costs
Adaptation can generate significant benefits in excess of its costs. Nationally, estimates of adaptation costs range from tens to hundreds of billions of dollars per year78,79 but are expected to save several times that over the long run (Ch. 29: Mitigation).80 The benefits and costs are larger in scenarios with high emissions. Formal benefit analysis is still in its early stages,81,82 and more research is needed to assess comprehensively the benefits of specific strategies being considered by individuals and organizations.83 Nonetheless, experience is growing. For instance, the U.S. Department of Housing and Urban Development’s National Disaster Resilience Competition required applications to conduct benefit–cost analysis including qualitative and difficult-to-quantify co-benefits, such as economic revitalization and other social benefits.84